51st U.S. Rock Mechanics/Geomechanics Symposium,
San Francisco, California, USA
2017. American Rock Mechanics Association
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ABSTRACT: The preparation of identical synthetic samples with the same morphological and mechanical characteristics allows for repeatable and reliable testing of discontinuities under varying conditions. Studies on the behavior of replica discontinuities to date have mostly been undertaken on laboratory shearbox apparatus, allowing for the characterization of discontinuity mechanics at low stresses. This study presents a new methodology for creating representative replica discontinuities suitable for testing under triaxial conditions, allowing for characterization at elevated stresses and temperatures. The advancement of computer aided design (CAD), three dimensional (3D) scanning and 3D printing has been used to design and create 3D printed molds in acrylonitrile butadiene styrene (ABS) plastic. Synthetic materials are then cast in to the molds creating cylindrical samples with a pre-existing discontinuity of quantifiable morphology suitable for triaxial testing. Statistical and visual analyses show the morphological characteristics of the synthetic discontinuities to be highly repeatable. In addition, the mechanical behavior of different synthetic compositions in unconfined compressive strength and triaxial is compared to the behavior of natural lower strength sedimentary lithologies. The behavior of the tested synthetic materials is found to not be representative of lower strength sedimentary lithologies, with stress-strain behavior showing failure in a quasi-brittle manner.
All rock masses contain discontinuities such as fractures, faults, joints, bedding planes and shear zones. Failure through intact rock is uncommon unless stresses are extremely high. The behavior and strength of the rock mass is instead commonly controlled by the behavior and strength of the discontinuities (Hoek, 1983). Triaxial testing of discontinuities was first undertaken by (Jaeger, 1959) and was used for testing discontinuity mechanics throughout the 1960s on synthetic replica discontinuities, artificially created discontinuities and real discontinuities (Raleigh and Paterson, 1965; Byerlee, 1967; Heuze and Goodman, 1967). Raleigh and Paterson (1965) also carried out some of the earliest work of testing discontinuities at elevated temperatures.
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